Field of the Invention
The present invention relates to an image capturing apparatus and a control method for the same.
Description of the Related Art
In recent years, major advances have been made toward improving the functionality of image capturing apparatuses such as digital cameras. Particularly in the field of solid-state image sensors, the obtainment of focus information by using a so-called on-imaging surface phase difference method has contributed to an increase in auto-focus (hereinafter “AF”) speed. The following is a description of the typical methods of obtaining focus information by using phase difference detection. Specifically, light that has passed through a portion of a pupil of the imaging optical system is received by a first light receiving element and light that has passed through a pupil region excluding the portion of the pupil through which light is received by the first light receiving element is received by a second light receiving element, and an image shift amount of the two images is obtained by a correlation calculation or the like. The direction in which an amount by which the focusing lens is to be moved can be understood by using the image shift amount of the two images, and thus high-speed AF can be performed.
The on-imaging surface phase difference method is a method in which light receiving elements that divide the pupil of an imaging optical system and receive light, are arranged on an imaging surface on a solid-state image sensor that obtains captured images. Currently, two main types of pixel configuration are employed for the solid-state image sensor on which such an on-imaging surface phase difference method is realized. The first pixel configuration is a configuration in which a pixel that receives light that has passed through a portion of the pupil of the imaging optical system and a pixel that receives light that has passed through a pupil region excluding the portion of the pupil through which light is received by the first light receiving element are arranged in a specific pattern among image capturing pixels that receive light that has passed through the entire pupil region. Also, the second pixel configuration is a configuration in which N (N being an integer of two or more) light receiving elements that divide the pupil of the imaging optical system into N are arranged within one unit pixel.
The first pixel configuration allows for the pupil region through which light is received by a light shielding structure of pixels or the like to be defined and is comparatively easy to manufacture, but the configuration is arranged by replacing some of the image capturing pixels, and thus these pixels cannot be used as image capturing pixels. Thus, there is a need to interpolate the signals that are missing due to this arrangement from adjacent image capturing pixels.
On the other hand, the second pixel configuration is difficult to manufacture because the unit pixel is divided into a plurality of light receiving elements by element isolation or the like, but pixels with the same structure constitute the image capturing pixels, and therefore non-uniformity from pixel to pixel does not occur. Also, the original captured image can be obtained by adding or averaging the signals from the divided light receiving elements. However, the number of light receiving elements is N times the number of image capturing pixels, and therefore it takes time to independently read out all of the signals from the light receiving elements.
In contrast to this, the technology described in Japanese Patent Laid-Open No. 2013-090160 proposes to resolve this issue by employing a configuration that includes a plurality of vertical output lines. Japanese Patent Laid-Open No. 2013-090160 discloses a configuration in which, in reading out signals from the plurality of light receiving elements included in the unit pixel via a corresponding plurality of vertical output lines, signals are read out via the same horizontal output line, in the case where the signals of the light receiving elements constituting one unit pixel are read out collectively.
However, as an extension of the technology in Japanese Patent Laid-Open No. 2013-090160, when reading out the signals from the divided light receiving elements on each of the plurality of vertical output lines provided for each unit pixel, only one of the signals from the light receiving elements can be readout via the vertical output line. For this reason, the signals from the pixels in a plurality of rows cannot be read out simultaneously, and shortening of the readout time is not achieved.